University Physics I - Classical Mechanics, 2019

Chapter 11
Simple harmonic motion
11.1 Introduction: the physics of oscillations
It is probably not an exaggeration to suggest that we are all introduced to oscillatory motion from
our first moments of life. Babies, it seems, are constantly rocked to sleep, in many cases using
devices, such as cradles and rocking chairs, that exemplify the kind of mechanical oscillator with
which this chapter is concerned. And then, of course, there are swings, which function essentially
like the pendulum depicted below.
F t
F t F G
v
F net
F G
F net
(a) (b) (c) (d)
Figure 11.1: A simple pendulum. In (a), the equilibrium position, the tension and gravity forces balance
out. In (b), they combine to produce a restoring force (in blue) pointing back towards equilibrium. In (c),
the bob is passing through equilibrium and the net force on it at that instant is again zero, but its momentum
keeps it going. At (d) we have the mirror image of (b).
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